"On the phone" refers to somebody's perspective, viewing somebody speaking into a phone. Over the phone refers to the specific method of communication in which you say something over the phone.
In...
just the difference in handset
Different kinds mobile phones have different battery capacities, receiver sensitivity, and signal strength, and some have a limited amount of internet capability as...
A phone is something you would use at home because its connected to your phone line, a cellphone is not connected to anything and you can take it where ever you go.