Can't update or install apps
This is a software issue. What I suggest is backing up your iPhone with iCloud backup (Settings -> Your Name -> iCloud -> iCloud Backup -> Backup Now - Unless it has already recently backed up), then make sure you get your wifi password and Apple ID password.

***If your Apple account sends you verification codes all of the time you need to add another number to your account in Settings -> Your name (or iCloud) -> Password &amp; Security -> Edit to add trusted phone number (you wont be able to get the code when you sign back in)>.

After you've backed up. Sign out of iCloud, erase the iPhone (Settings -> General -> Reset -> Erase all Content And Settings) and then set up the phone, but restore from the iCloud backup. You'll need wifi, Apple ID account login (and a verification code from another trusted number if your account sends you verification codes). Once thats done the phone will look the same, messages, apps, photos, notes, calendar events, etc.

After that, then try to update your Apps.