Is the IMEI# on the back of the phone?

Yes but it is much easier to read and copy by:

1. Go to Settings > General and tap About.
2. Look for the serial number. You might need to scroll down to find the IMEI/MEID and ICCID.
3. To paste this information into Apple registration or support forms, touch and hold the number to copy.

Source Find the serial number or IMEI on your iPhone, iPad or iPod touch – Apple Support