Is your phone an Android? And do you do Google searches? And do you have a Gmail address? Android is owned by Google. In order to download phone apps, you need Google Play. So that Google Play connects with the Google Search, which connects with Gmail to tailor your ads.
What really pissed me off is that I use my Gmail (also Google) to type up To Do lists for myself. Usually, if I need to buy stuff, it goes on the list. Several weeks ago, I needed to go to a few stores, so I even wrote at the top of one list: Dollar Tree. Not dollar store, but the actual name of the dollar store.
Two days later, I'm on my homepage for YouTube (also owned by Google.) Suddenly, I'm seeing video suggestions for Dollar Tree hacks. Not dollar store hacks, which I've seen before, but actual Dollar TREE. That's when I realized Google culled my private EMAIL/To Do List to give me YouTube suggestions.