Minecraft trap door build items?

Hi, I'm playing Minecraft on my phone. On YouTube I see all the time people who are playing on the computer put flower pots on trap doors or something else as decoration. I then tried it on my cell phone, but instead of putting objects on it, it opens and always closes the trap door.

does that not work on the cell phone? Or am I just too stupid for that? 😅

You just have to sneak while you do this

What?

Sneaken = slouch or squat down. On the mobile phone this is the button where you fly to the next in the creativ game mode.