Traditionally you have either a tone remote or a DC remote. One uses in-band tone signaling, and the other uses DC voltages, to control a radio at a remote location. It could be a radio in another room or at a location like a mountain-top radio site. The remote is usually a telephone-like device (Google "Motorola DGT9000"). This is helpful in large buildings where you can put the radio in the penthouse and run a phoneline to an office several floors away. No worries about getting a signal out or in that way.
So, no, you wouldn't use a portable radio with it. In a situation where a portable can't talk out (of say, a building) you use what's called a BDA or Bi-Directional Amplifier.