First, need to determine if it is the pump or the steering unit. I don't have my shop manual in front of me, but the pressure will be in the 800 to 1200 PSI range. To test it you need to adapt an appropriate gauge to the pressure port and start the engine.
If you don't want to go through the pressure test, you can do a short cut test, not very safe, not good for the hose, but... With the engine at slow idle, clamp the pressure hose with vice grips, listen for the pump to load and the engine to slow or stall. Be sure to clamp the pressure hose, not the return! (The pressure hose comes off the machined body of the pump. The return is attached to the reservoir.)
If the pump is not building pressure, it will need to be replaced.
If the pump is building pressure, the problem is in the steering unit. It is repairable. You will definitely need a repair manual though!