A phone in your hand doesn’t mean you’re reachable
Being on your phone and being reachable are not the same thing at all.
I have two acquaintances with completely opposite habits. One almost never takes out his phone. If he’s talking to someone or looking at something, he is fully present, and the phone stays in his pocket. The other practically never lets go of his: chats, Telegram video messages, videos. He is always filming something and sending it to someone.
And yet you can message the first one and get a reply within seconds. Call him, and he picks up after one or two rings. The second one can go hours without noticing a message and miss ten calls. With the phone in his hand.
You would think it should be exactly the other way around.
Maybe the phone simply plays different roles for them. The first one takes it out, replies, and puts it away again. For the second one, something is always happening on the phone. You can be recording a Telegram video message in one chat and completely miss a message in another. From the outside, the person is clearly online, but his attention is already taken.
I think for the first one, the phone is like a doorbell. If it rings, someone is there. For the second, it is more like a noisy train station: something is making noise there all the time, and one more signal easily becomes part of the background noise.
Being on your phone and being reachable are not the same thing at all.