The 'phantom penis' is not common, in fact very uncommon, in trans women who have GRS...after a period of settling in when all the nerves reconnect up.
I long had a phantom vagina and only 3 days after GRS I could clench it.... but I kept interpreting stimulation of my clitoris as stimulating the head of my old penis ..which it originally was of course.
That slowly faded away over the next 2- 4 months, as all the nerves connected up and the stimulation sensation settled into more of a single (albeit more generalised) physical point, which is an interesting period to go through., you keep getting these 'shocks' (like from static electricity) randomly.
So post GRS there is this rewiring/remapping going on. In my case it was only partial as my vagina mapping was already there and even the 'penis like' sensation was more of a disembodied one, rather than feeling like I actually had one.
There have been studies on this and whereas cis men who lose their penis commonly report having a phantom one, very few trans women do post GRS (after settling in of course).
Just transitioning doesn't solve all your problems, in fact it often causes many new ones. BUT, it does mean you can handle things better. I emotionally deal with issues far better now than I did in the past. I am more resilient because I don't have this gender dysphoria (GD) 'noise' going on in my head all the time.
The younger you transition the better the outcome because you haven't had all those years (decades) of suffering GD and you have less 'unlearning' to do when you transition. The latest studies on this are quite clear, young transitioners have near identical mental health to their cis peers ...an amazing improvement over those who cannot.
BUT, cis people tragically commit suicide as well for a whole host of reasons. We can only speculate about what Jamie was going through but the research shows she had a far better chance of survival by transitioning than by not, however it is no guarantee.