I realize I probably don't have the right to make Philly's being southern and all, but my husband was born in Niagra Falls, NY, & grew up in PA. We found a place here in San Angelo, TX that actually made good Philly's. Then they changed cooks, and you know the rest. Through trial & tribulation, I finally found the right balance of ingredients and we all are very happy to have Philly's again. I also realize there are many ways to make a Philly, especially cheese wise, but this is my recipe & I make them several times a month. Hope you enjoy.
Saute onions & bell pepper with small amount of olive oil, I use an electric griddle. (If I had a gas stove I would use a cast iron griddle on the stove top, oh well). Once these veggies are tender, add mushrooms for a short time only, (mushrooms cook extremely fast).
I remove the veggies and cook my Ribeye, breaking it up into pieces with my spatula as I brown it. This only takes a few minutes, then add veggies back on griddle & combine with ribeye.
If you use sliced cheese, layer it on bun and place meat & veggies on top. You may need to pop the sub into a hot oven for a couple of minutes to throughly melt the cheese. If you melt the cheese in a sauce pan ahead of time you can just spoon it over top of the meat & veggies. Either way works fine.