Simple Validation using PHP

What's a good way to do simple validation against data contained on the i
from a PHP program? I'd rather not invest in having to prepare, param, and
execute a stored procedure when all I need is a simple true or false. I
have functions (implemented as procedures in a service program) that
returns what I want, but I'm having trouble executing that function from
PHP. I don't have a problem with a stored procedure that returns values or
a stored procedure that returns a result set.

Is there something special/different about functions?

Thanks!