FaceTime not working on my iPhone

Re: Why my phone no is not working with face time

FaceTime uses wi-fi if you have a strong signal,

or

you may want to use cellular data (charges may apply) if it is turned on:

See how to: View or change cellular data settings on iPhone - Apple Support

You can also see how to: Add or remove your phone number in Messages or FaceTime - Apple Support

and

Use FaceTime with your iPhone or iPad - Apple Support for tips

Eg: says:

Turn on FaceTime 

Open the FaceTime app and sign in to your Apple Account.

You can also do this from Settings > Apps > FaceTime. 

If you’re using an iPhone, FaceTime will automatically register your phone number.

If you’re using an iPhone or iPad, you can register your email address:

1. Go to Settings > Apps.
2. Tap FaceTime, then tap Use your Apple Account for FaceTime.
3. Sign in to your Apple Account.

Trouble-shhooting: If you can't make or receive a FaceTime call on your iPhone or iPad - Apple Support

Support if needed:

The FaceTime Support Team's Website: FaceTime - Official Apple Support