Phone has stopped waking up when I raise my wrist.

Are you asking about your phone? Or your watch? If you're asking about the Watch, check to make sure you don't have Theatre mode turned on. Access the Control Center on your watch by swiping up from the bottom of the screen. Look for the button with the two masks. If it is highlighted, tap it to turn off the feature.

Use Control Center on your Apple Watch - Apple Support

Here you go! You can simply enable it again.

Use Raise to Wake on your iPhone – Apple Support

Glad it helped!