φ-features, θ-roles, and ∅ pronunciations
Just to clarify, since I’ve talked to a couple of people so far that have had some (perhaps momentary) confusion on terminology: Agreement features (person, number, gender) are often referred to as φ-features—that is, “phi features.” The role a DP plays in an event is determined by the θ-role it gets (that is, “theta role”). And ∅ represents something silent, which we will often call “null” or “zero”.
Just to be clear, even though each of these (∅, φ, θ) is drawn as a circle with a line through it, they have distinct names (null, phi, theta) and meanings, and you want to keep clear which one is which.