Most Modern Phones have the antenna built into the body of the phone. Ancient phones like the Ericsson SH888 (my first phone 1998 ) pictured below have an external antenna.



A trick to increase the antenna gain would be to get a old coffee tin can or something similar and at the centre of the base of the tin a small hole large enough just to insert the cell phone antenna would be made. Pointing the tin and cell phone at the base (just slowly rotate through 360 degrees at the highest available point until the signal strength meter indictated the highest signal strength) would dramatically increase the cell phones range.
Its a similar technique to the long distance mesh networks being created in Africa.
Sadly though most phones do not now have external antennas.