...security and encryption on any mobile device don't matter anymore.
This isn't true in at least the following ways:

1. Encryption isn't useless.
   The "big guys" (i.e. state-sponsored agencies like the NSA and CIA) constantly develop methods to compromise mobile phones. But that is NOT the same as mass surveillance. At least not yet. For your encrypted data to be compromised by an attack against your personal device, rather than by being routinely captured as it travels online, you have to be a person of interest. You have to be targeted specifically. That's expensive to do. In the future, it will become cheaper and more routine, but that doesn't mean encryption is useless. Documents from the FBI, NSA and others show that the rise in the use of encrypted communications frustrate their efforts. It is also the reason the Russian government has banned using Telegram. It's because encryption works. The post above suggests this wouldn't be necessary if it was so easy to get past it.

2. The NSA and CIA aren't your only adversaries
   State-sponsored agencies are not the only adversary you should be protecting yourself from. Black hat hackers and corporations are also after your data. Using encryption thwarts their efforts as well. For example, if you store your data on other people's servers (e.g. email or your backed up/synced files) it is much safer and more private if you use encryption (where you hold the key, so zero-knowledge or end-to-end encryption). Firstly, it prevents the owner of the server reading and harvesting your data. Harvesting your personal data is the basis of, for example, Google's business model. Secondly, if those servers are hacked, the hackers can't read your stuff. This is why it is safer and more private to store your stuff with Protonmail or Tutanota instead of Gmail and Spideroak, Sync.com or Tresorit instead of Dropbox, Google Drive or OneDrive.

3. The comment above focuses on mobile, but this is misleading. Everything I've written above is equally true about desktop computers too. Windows, Mac and Linux are all constantly the subject of state and other hackers. There's no doubt that the enormous resources of the NSA and its kind will always win if they are leveraged against you. But that doesn't mean the answer is defeatism and giving your data over willingly to anyone and everyone. You can make a meaningful difference to your privacy and security by using encrypted messaging, email, disk and file storage.

Popular apps and their encrypted alternatives

Depending on your use case, you might not find an encrypted alternative for everything you regularly use. But you will find encrypted alternatives for a lot of it. Here are some suggestions:

File storage:

Ditch services like OneDrive, Sugarsync, Dropbox, Box.com and Google Drive. They either don't encrypt your data or they encrypt it in a way where they have the key, which is meaningless for your privacy. They also have a track record of cooperating with the NSA and other law-enforcement agencies.
Altenatives:

• Spideroak - US, zero-knowledge, low prices
• Sync.com - Canadian, zero-knowledge, very much like Dropbox in its functionality
• Tresorit - Swiss, expensive, but excellent. Supports 2FA and all OSs.
• [Cryptomator] - Open source and free. Not a service but lets you encrypt files locally before syncing via any other service.

Email:

Switch away from Gmail, Outlook.com, Yahoo and any other service that offers you email "for free" (including your ISP). Your emails are not encrypted, they are not stored encrypted and their content is visible to everyone who has access to the servers that email sending uses. None of these companies deserve any more than a minimum score in privacy terms; all have access to you data, Gmail harvests it to profile you and make money from ads. But the worst offender by a country mile has been Yahoo.com, who had literally billions (with a b!) of accounts compromised, failed to tell their users and, separately, intentionally created spyware for law enforcement to trawl through users data. Encryption makes this impossible.
Alternatives:

• Protonmail - open source, Swiss privacy laws apply
• Tutanota - open source, German-based, supports encrypted email search
• Mailbox.org - German, includes calendar, contacts and PGP key import
• Posteo - German, includes calendar, contacts and PGP
• Nextcloud - not encrypted by default but can be used with encryption addons for emails and files
• Mailvelope - not a service, but an browser add-on that can be used to encrypt/decrypt emails sent by almost any service. (Note: this will not encrypt metadata, only the body of the email)

Messaging apps

SMS messages travel through the internet / phone network in plain text, just like regular unencrypted emails. They are also the subject of mass surveillance by the NSA, GCHQ and, probably, other surveillance agencies. It is even possible for regular people to buy devices that imitate phone masts and intercept such messages by tricking your phone. Encryption helps you here, too.
Alternatives:

• Signal - open source, free
• Whatsapp - uses Signal's encryption
• Threema

Skype / Google Hangouts

The NSA and others have routinely recorded Skype calls and probably record or subpoena videos from other services too. There exist several, very good and easy-to-use alternatives that use end-to-end encryption.
Alternatives:

• Wire - Swiss, open source, end-to-end encrypted
• Jitsi Meet - open source, end-to-end encrypted. Easiest thing to use ever.

Slack

Same problem: no privacy/security
Alternatives:

• Peerio - open source, encrypted
• Stackfield - Swiss privacy + encryption
• Secure Chat

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There are many other services and alternatives that use encryption to protect your privacy. In general, if you can, try to favour: open source software (there's more security if people can inspect the code), services you pay for, not services that use your personal data to sell to advertisers (check how they make money), services that use "end-to-end" encryption or "zero-knowledge" models. Enable 2-factor authentication on your accounts. Don't re-use passwords on multiple accounts; manage complex passwords through Bitwarden or a similar, open-source and encrypted password manager.

Don't buy into arguments that just because the NSA have the resources to get into your phone that there's nothing you can do to protect your privacy or that encryption is useless.