It sounds as if the drain pump has seized. On Whirlpool belt drive washers the pump can seize up, but the belt can still slip on the pump pulley allowing the rest of the mechanism to operate.  Since the machine can't drain, the pressure switch remains satisfied and the circuit to the spin solenoid will not energize.  The machine will just operate in neutral during the spin phase.  

Depending on which portable you have you may be able to manually free it by hand without too much work.   If you have the larger convertible model there is a rear access panel.  Remove the panel,and loosen the motor mounting bracket to relieve tension on the belt.  Now you reach under and around the right sideof the transmission  and try turning the pump pulley by hand.  Try turning it in the opposite direction from the norm to see if it frees the impeller.  If not you either need to rebuild or replace the pump.  

If you have the smaller unit (later models) youhave to remove the entire cabinet to access the pump.  That is complicated and requires review of the appropriate service literature.  Check the Ephemera library for Whirlpool service manuals.  You can also search the site for a thread regarding this procedure (not sure if one exists).  

Good luck and keep us posted.