I'm really curious - what people did you get this idea from? I've never heard this before. I have heard "mainland China" to mean, specifically, "China, not Hong Kong or Macau", from:
- Taiwanese people
- Hong Kong people
- Mainland Chinese people
- Taiwanese-americans
- Chinese-americans (immigrated from the mainland)
It's just mainland China (大陆). I have never met Chinese or Taiwanese people who feel this is a politically loaded term.
Out of habit, I keep my phone off during the flight and turn it on after clearing customs.