SQL & PL/SQL :: ORA-00904 EID Invalid Identifier

I'm having an issue creating a table which references a larger table of mine.It gives me the error:

ORA-00904: "EID": invalid identifier

when issuing the command:

CREATE TABLE Phone (P_num CHAR(7), P_type VARCHAR2(10), PRIMARY KEY(P_num), FOREIGN KEY(EID) REFERENCES Employee ON DELETE CASCADE);

I need the employee id (EID) to be the primary key for my table Employee, as described here:

DESC Employee;
Name Null? Type
----------------------------------------- -------- ----------------------------
EID NOT NULL CHAR(7)
E_NAME VARCHAR2(15)
E_ADDRESS VARCHAR2(30)

And since Phone has its own primary key of Pnum, I find it weird that it won't let me reference Phone back to Employee using EID.