Welcome to our forum.
(I hate the salesperson term!)
Polo shirts with the company logo are fine. Big Johnson T shirts are not.
First off, leave your personal cell phone with your other belongings. Nothing ticks me off more that a cell phone ringing while I am having a conversation with a salesman, especially if he takes the call. If you don't mind interupting our salesman/customer conversation then you don't mind losing a sale either.
This is my biggest peeve about shoppers. I think they should turn off their cell phones when they enter the store. Especially when its busy and I could be helping someone else. I feel it shows no respect for me to take call after call while I am presenting my product. I really dont mind someone taking a quick call, but someone that takes 2 or more 3+ minute calls upsets me.
I was going to go down that road, but since you already did, I'll just give a big fat DITTO. I don't know what makes customers think that just because you are a sales person that you deserve less respect than other higher beings. As for dress, I don't think there is anything wrong with a clean pair of nice jeans. However they have to be at waist level (already stated) and a nice shirt, button bown oxford or polo style. You're right. Cell phone etiquette goes both ways, as does common courtesy, manners and respect.