If the request is simple and might take a few minutes do it out of good will and score brownie points. If it’s bigger, then just say it’s out of scope and can be addressed in Phase 2 with a new cost estimate. Clients’ need to hear adding scope creep to the web project will jeopardize the current progress, complicate matters and complicate deliverables and resources assigned. If the clients still make things difficult, just say I’ll check with the boss – from that point on it’s a business call for the business owner.