None of my apps in iPhone work unless I’m connected to Wi-Fi

In addition to Nick's good advice, please make sure your phone is allowing individual apps to work on cellular if WiFi is not available. WiFi is the default.

Set cellular data use for apps and services

Go to Settings > Cellular Data, then turn Cellular Data on or off for any app or service that can use cellular data.

If a setting is off, iPad uses only Wi-Fi for that service. I hope this helps.

Have you any cellular reception? You might want to try to restart the iPhone to see if the issues persist