Hi I have a ttl clock signal that id like to change the phase of to see if it changes effects the unit under test (not relevant but its a digital transmitter and an automated testing setup) this way I can see if longer bnc cables would cause issues (because of how it changes phase). What sort of circuit would I need to make or what equipment would I need to buy to achieve this? It is fairly fast like 50 MB/S.
Consider a programmable delay line or programmable timing element. These are ICs which can apply delays to a clock signal, and can be controlled by a microcontroller to vary they delay they apply.
You will need to choose a chip based on the delay range and resolution you need, but to give an example, the Maxim DS1124 would be suitable for 10MHz clock signals, and con be programmed over SPI.