His perspective
When He Reaches for the Phone Instead of You
He may be trying to come down from the day. You may be waiting for the one moment he will turn toward you.
You get into bed and turn toward him. His phone comes out. It is such a small thing to object to that you might say nothing, then lie there feeling alone beside him.
He may be trying to decompress rather than choosing the screen over you. He might even think sitting together is a form of closeness. That explanation can be true and still leave you without the attention you were hoping for.
Ask for the moment you miss
Tell him which moment you miss. “When we get into bed and the phone comes out straight away, I feel the evening end before we have been together.” You are asking for a way to find him, not an inspection of his device.
A return is more useful than a ban
He can have time to switch off. You can ask for a return you can count on. Agree on a short time to talk or sit together before or after the scrolling, and see whether the agreement is kept. If every attempt to ask for attention is dismissed, the issue has grown beyond the phone.