Hi everybody. Can someone help me finding a solution for this problem:

"Let M be a model and phi(x) be a formula with parameters in M, x being a single variable. Prove that if phi(M) contains the parameters of phi(x), then phi(M) is not an elementary substructure of M."

I'm not even fully understanding the problem, since I can't figure it out what the "parameters of phi(x)" are.

Thank you so much

bye!