The thing about an old pump, be it phantom, cocker, etc is the requirement to have good technique and coordination. Many of us learnt/honed our skills on this type of marker because we had to; nothing else was available at the time. If you are patient and put the ground work into understanding the marker then in the longer term it will probably make you a better paintball technician. Your immediate problem is you'll be coming up against players who at the flick of a trigger can lay down way more paint than your phantom ever will, and that can be disconcerting.
I think your brave to start with a pump, but good luck and stick with it if you can, for as long as you can.
My personal route has been Splat, Sheridan Pump, Razorback Pump, WGP Cocker, Mini Mag, Mini Cocker, Bob Long timmy Classic, Bob long 2k2 and Species, then a 5 year break from the sport, now I'm back, its with a proto reflex rail (soon to be DM12), and a WGP Pro Trilogy Pump and Cocker and thoroughly enjoyed the journey so far.
So don't think owning a pump is a reason others would think they can point and laugh. Have fun with it and move on when you are ready.
Best of luck.
Regards,
Colin.
Split Personalities