Restart the iPhone 1st. Most of the time that encourages it to look for the network. How you know if it works is if 1 app is updating. If you have folders you'll need to look for that app and see if its in a pie like circle and is moving. If non of that occurs then delete the apps and then reinstall them (I'd do a backup 1st). If you cant reinstall them then sign out of iCloud and then sign back in. Reseting network settings is a good idea as well but you will need to know your password for wifi.
If none of that is beneficial then the last resort is to back 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 & 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.