voicemail, wifi calling

I'm on the Go5G Plus, planning on trip overseas (Philippines) in the near future. I have conversations w/ several Tmo reps mostly from Philippines primarily because of the times I call, but then I almost always thought of a follow-up question/questions after I hung up. Tried to research on my own thru the community forum but most of the questions/answers  are from several years ago or recent ones that's not pertinent.

I need confirmations or corrections to avoid coming back to avoid gigantic phone bills:

 > if I leave the phone OFF, incoming calls would automatically go to voicemail and I will not get charged.?

> how do I listen to my voicemail w/out incurring charges?

>on W- fi calling, turn off Mobile data, Wi-fi and Wifi calling ON, calls to US are free, but if you use Wi-Fi   to call local# then I will get charged?

need help and advice...