Can I connect an Apple TV to my phone hotspot

Your Apple TV will accept hotspot connectivity just like any other Wi-Fi network. It is indifferent about how it gets internet.

You mobile provider may have different thoughts about that. See their terms and conditions. They measure hotspot use separately, and that may be capped at a max well below what is useful for daily TV watching — or worse: excess use may be billed separately. It all depends on which plan with which mobile provider. Don’t assume ‘Unlimited’ is really unlimited.