Well done for progressing so far on your own. That is really impressive.
You sound as if you have reached a block, which is understandable, as moving to doing gradual exposure therapy using urinals is a very big jump. I assume that you are locking the cubicle door. If so, what I suggest is that you work on these stages:
- unlocking the door but leaving it closed. The fear here is that someone will barge in and wonder why you are standing and peeing. In actual fact blokes do use cubicles to pee, usually when they would otherwise have to stand next to someone at a urinal. This is very much the case in small two urinal toilets, and in busy toilets. The second fact is that rather than comment, he would retreat hurriedly saying nothing more than "Sorry mate".
- Having door slightly ajar
- Paying no attention to how open or closed the door is.
When you have got to being 80% reliable with the door swinging freely, or open, only then do you consider using urinals, and even then, look for large quietish toilets: e.g. motorway service stations, shopping malls.
Another technique you need to use is what we call "faking". For instance, if the thought of not locking the cubicle door is highly anxiety making you, do this instead. Make sure you do not need a pee; go in and doing everything as normal, as if you were going for a pee. Cos you don't need one, there is no anxiety about having to pee. That leaves you to deal with the anxiety of the new situation. See how it feels, explore the feelings and the fears, look for evidence to back up your fear and realise you can't find any. Repeat the faking exercise several times leaving an interval to calm down. You will find that eventually you will lose most of the anxiety about the situation; only then introduce the peeing.
Faking also gets you used to standing there not peeing, which is good, as we all find we need time standing there to relax before the flow starts.
Enough for now, let me know what you think of this.