creep up on someone
— phrasal verb with creep us/krip/verb [ I always + adv/prep ]
to approach someone quietly, so that the person is suddenly surprised:
Did you have to creep up on me like that?
If an event, day, or condition creeps up on you, you are surprised by its arrival, esp. because it has come gradually:
Budget time is creeping up on us and if we don't put in a proposal we're not going to get the money that we want next year.