Please help me I'm mutating and I don't even know it!

I'm at my wits end..
I have a trigger which works fine before insertion, but fails with the following error on update:

ERROR at line 1:
ORA-04091: table TEAMING.PHASE is mutating, trigger/function may not see it
ORA-06512: at line 4
ORA-04088: error during execution of trigger 'TEAMING.PHASE_UNIQUE_CHECK_AND_ID_GEN' Cutting down the trigger to it's simplest point where I still get the problem, it looks like:
SQL> create or replace trigger phase_unique_check_and_id_gen   2 before insert or update on phase for each row   3 declare found number;
  4 id number;
  5 begin
  6 select count (*) into found
  7 from phase where (
  8 :new.release = phase.release);
  9 end;
 10 /
On a table that looks like:

SQL> descri phase

 Name                            Null?    Type
 ------------------------------- -------- ----
 PHASE_ID                        NOT NULL NUMBER
 RELEASE                                  VARCHAR2(8)
 MILESTONE                                VARCHAR2(16)
 ACTIVITY                                 VARCHAR2(16)
 EXEC_TYPE                                CHAR(1)
 STATUS                                   CHAR(1)
 DESCRIPTION                              VARCHAR2(256)
 MARK_FOR_DELETE                          CHAR(1)

Can someone please show me the error of my ways? Help Mr. Wizard.. I don't want to be a mutant!!

					Thanks
					Symen Blumenfeld