2 meter phone patch was a huge draw for me in the mid 70's. That is what lured me into the hobby. I recall our club having 2 repeaters on a broadcast tower and having to have an additional receiver on the output frequency. In those days, if someone was on your output frequency, your repeater could not come up and interfere with them thus the need for the system to monitor the output before transmitting.
I also recall one bright fellow who programmed a Commodore Pet computer to control both machines. With TouchTone pads, you could make an autopatch or play a couple of welcome tapes from broadcast cart machines. That was VERY cool back then.
The same guy, Jack, KB4B, helped me start a repeater using his BASIC code modified for my one machine and his schematic for the computer-to-repeater interface. He even threw in most of the parts and charged nothing for any of it. I added some additional features like being able to tone up NASA Select audio so that we could listen to the space shuttle via my backyard C-band dish and I also made use of one of the "voices" in the computer to generate the CW id. The machine consisted of 2 Icom 22-S transceivers, some VHF Engineering 220mhz gear and a couple of yagis (to link the split sites), 2 Hustler G6 antennae and a Commodore 64. Audio mixing was accomplished with an old Radio Shack stereo audio mixer, left channel for audio to the repeater, right channel for audio to the phone line. Some simple EQ on each input allowed me to have very nice audio unlike some other linked repeaters that sounded "tinny." The whole machine was as ugly as a mud fence but worked beautifully.
A marine deep cycle battery on constant charge ran a voltage inverter which, in turn, powered the station and provided continuous operation when AC power failed. Not the most efficient power chain but it never failed once in the many years the repeater was on the air.