My iPhone keeps saying no cellular data

Try to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

See these Apple articles below:

Manually update your carrier settings on your iPhone or iPad

Manually update your carrier settings on your iPhone or iPad - Apple Support

Update your network provider settings manually on your iPhone or iPad

Update your network provider settings manually on your iPhone or iPad – Apple Support (UK)

Looks like you don't have Service (?), see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

Do you have a SIM card in the iPhone?

Check also here -> If you can't activate your iPhone or iPad (Wi-Fi + Cellular)

If you can't activate your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

• If you still can't activate your iPhone or iPad, contact Apple Support.

This happened to me too. I had no cellular data all yesterday eve. This morning it briefly worked then stopped working again. After contacting Apple Support I ran it in restore in recovery mode, which I was assured would fix the problem. It did not. Now I have a screen-wide error message and my only option is to shut down. The phone is completely useless. I have to bring it in tomorrow to see if it's fixable. Wondering if one of Apple's updates did this. I made ZERO changes on my end. Not happy.

Contacted my carrier first. It is an Apple problem. I've seen it pop up on several community boards after searching. My phone is barely two years old and one minute was fine, the next it was not.

Have you checked with your carrier to see if they report a local outage? And checked up on them here→Down Detector - Crowdsourced Outage Check

What happened when you connected your phone to your computer and updated or restored it, as described in the Related Article at the top of this page?