A phrase referring to when someone's whining, grumbling, complaining, etc. The mobile refers to the device often hung over a baby's cradle for their soothing entertainment, as it spins around. Thus, "getting him (the complainer) a mobile" implies he is a cry-baby.
Mr. Truscott had to listen to all of the crying pleas of the physical education student, but then Marly quipped, "Hey, GET HIM A MOBILE" and Kemberling and Herzog were astoundished by this, as was the entire class. The gym student was INSTANTLY SCHOOLED!
More popularly identified as Triumph The Insult Comic Dog from Conan O'Brien, THAT Fucking Dog (TFD) certainly knows how to work an audience. Surely, you've heard his wise jocularity in regards to how often he schools MBNA employees, such as Bailey aka Shrek. UNDERAGE BEEE-SEAN!
TFD Often utters the line, "What kind of legs does she have?" Promptly, S.B. becomes excited, but knows he's inferior to Dusty and the rest of Citibank employees' 7.5 inch cocks.