(utilt is usually a bad move, but it works ok on ROB to send him into the air),
First of all, I extremely disagree with this. I think utilt is a great falco move that's quick with tons of priority, which isn't used enough.
On topic to the thread:
When ROB is on the ground, his tilts outrange you. When you find yourself in the situation where you both are on the ground and you're near/on his tilt range, I reflector. I feel like ROBs are very sesceptable to the reflector and space back quite a bit; I usually approach at this time.
Unlike other people said, I feel that when ROBS are above you they know they're at a disadvantage. Most of them bair for spacing as it comes out quickly and is difficult to punish when they're descending. Learn the range to the bair so you can send an upsmash right into his anus when he lands.
When you fly off the stage, three things will happen (in my cases).
1) They will run off and try to gimp you
2) The ROB will stay on the edge and SH-bair you when phantasming back onto the ledge, usually killing you.
3) Shoot a laser/top
Because of this, when I feel like they're not going to try and gimp me I immediately reflector after being hit to avoid any projectiles. I always phantasm on the ledge, because ROB's bair outprioritises it if tried to phantasm on the stage.
I kill robs in usually two cases. One, I punish their landing/them in the air. Two, after being tripping I predict an fmash based off of where they rolled from previous times they were tripped.
SHDL, and good luck.