Why when I press speaker I lose service?

Hi,

Does the handset still ring on an incoming call?

Do you hear dial tone when you lift the handset from the cradle and press the speaker key?

If no to both the above then there may be a problem with the phone’s loudspeaker, which can cause other problems.

Does the speaker icon appear in the display window when you press the speaker key?

Have you tried resetting the handset to check if this resolves the problem. Not sure if this will delete any stored information or not in the phone just so you are aware that it might do this if you reset it.