“Welcome to the team! It’s great to have you with us.”
You just hired a new employee. She comes in for her first day of work. You say this to welcome her.
Welcome to the team! It’s great to have you with us.
Use this phrase when a new person joins a team that you're part of: a sports team, a company that you work for, etc. You can even use this phrase jokingly in situations like when someone marries your brother or sister:
Welcome to the team, Frank.
Use the phrase "It's great to ___" in social situations to say that something makes you happy:
It's great to see you.
It's great to finally meet you!
More specifically, you can use the phrase "It's great to have you ___" to talk about someone's current situation:
It's great to have you back.
It's great to have you as part of the family now.
It's great to have you with us.