verilog code about shift phase 0, 90, 180, 270

If this is a homework problem and you are truly limited to one clock, they may be looking for you to derive your own clocks using a single clock at a rate 4x what you need.

If this is a real application, then the answer is you probably want to feed your one clock into an ALTPLL to produce at least two clocks (for 0 and 90 degree phase shift) and then use both edges of each of those clocks to produce the 180 and 270 degree transitions.