Use same iCloud for personal and work phone?

My friend currently has his personal iPhone and he recently purchased another iPhone to be his work phone.

His employer does not have access to the phone. He just wants a fully separate phone for all of his work contacts.

Would it make sense for him to use his personal iCloud on the work phone? Or should he make a new completely separate iCloud?

There are no concerns with his employer, accessing his information, it’s entirely his phone, but I am wondering if this will screw up his texts/imessage and stuff.

The phone will have its own SIM card and both phones will have their own unique phone number through different SIM cards.

I am asking for help here as he requested my help to get his new work phone set up this afternoon and I am unsure if he should use his same iCloud or create a new iCloud.

Again, although it’s a “work” phone, it’s technically a second “personal” phone which he will only use for work.