You heard wrong. Phuket is one of the worst entry points. Most of the land borders are OK but don't do same day in/outs (except with the help of an agency at specific borders such as Ban Laem).
They got a lot harder on people staying on endless visa exemptions/tourist visas etc years ago, that is, a couple of years before Covid (around 2017 or 2018).
Things have continued to tighten up further in more recent times. However, we've been hearing of the occasional denied entry since at least 2015 and this has only intensified over the past few years except during Covid when almost no one could come in of course, and immigration was more flexible towards those stuck here.
No, you can't. You do it once. The second time you're going in person for an extension and why would anyone report on day 360 when they have to leave the country anyway?
You can, in practice, only do ONE online report for a 360 day DTV stay, which is on day 270.