Foamy power steering fluid

Foamy is usually a sign of air in the fluid, most times because it is low. It can also be from contamination as well. First thing I would do is check the fluid level. If it is full then I would flush the system to get clean fluid into it. If it is low then it's likely you have a small leak, possibly in the steering rack. They can leak out into one of the bellows and you won't see a leak unless it fails and spills the fluid.

For a fluid flush, go buy a gallon of the GM power steering fluid.
With the engine off get the front tires off the ground so you can turn them by hand. Block it there so it's safe to go under it.
Get a drain pan and put it under the power steering return line on the pump. This is the rubber line going into the reservoir on the side. Item 4 in the image.
Remove the line and let the system start to drain.
Plug the return line port on the reservoir.
Now turn the steering wheel fully left and right while having someone monitor the fluid level so it doesn't get low. Keep doing this until the fluid coming out looks clean like that which is going in.
Remove the plug and reattach the return line to the reservoir.
Now be sure the fluid is full and bleed the system.
To bleed the system, start with the engine off, turn the steering wheel lock to lock 12 times while being sure the level is full.
After that start the engine and turn the wheel lock to lock twice. Listen for any strange sounds or whines. Shut off the engine, set the car back down and check the fluid level.
Now see if there is still a problem. Some foaming will be normal until it is warmed up.
Once the engine and steering are warm, check the level again.