use of alias

Hello Everybody,

I am trying to change a oracle function to postgreSQL. I have to use the
function parameter in different query so i need to use alias command.
but i am not able to use this alias in "from clause" of select statment.
could anybody please let me know how can i use it in from clause.i am
getting following error while executing the funciton..

MT ALIAS FOR $1;
ST ALIAS FOR $2;

select count(*) into count1 from MT,ST where MT.phonenumber=ST.phonenumber;

*ERROR: syntax error at or near "$1"
LINE 1: select count(*) from $1 , $2 where MT.phonenumber=ST.phone...

Thanx in Advance for all of your suggestion....*