I'm a school safeguarding lead. Issues arising on sleepovers that I have then had to deal with due to it being reported to me or causing issues in school include
A child taking covert pics of another child getting changed and then circulating them on whatsapp
Children lifting images of school staff from the school website and using them to make obscene images/videos which were then circulated on social media
Children sending anonymous, threatening messages to a child who was not on the sleepover as a "joke", causing said child to be so distressed she self-harmed
A child being so distressed after being shown a video of someone killing themselves that she required counselling
These are just a handful of examples. A drop in the ocean.
In an ideal world 10 year olds wouldn't even have smartphones, and children who are old enough to have smartphones would have parents who put limits and robust parental controls in place. But since experience tells me that many parents fail to set any boundaries or restrictions around their kids internet use, this isn't something you can leave to chance if you want to safeguard your DC and the DC you're inviting into your home. So, OP in your shoes I would tell parents upfront and in advance that we have a house rule, phones stay downstairs overnight. Don't spring this on them on the day of the sleepover.
I would make clear that any of the kids are welcome to wake me up at any time, however many times they needed to, if they were worried about anything or wanted to contact home. I would also reiterate this to the kids directly when they arrived and before they went to bed.
Any parent/child who didn't feel able to accept these conditions would be free to decline the invitation, that's their right. But since I'm responsible for managing the risks to any child who comes into my home, I also have a right to set that boundary.