We have all played in those gyms that have minimal space behind the back line for serving.
You are allowed one-step into the court during your serve. However, you still must start your serve motion behind the line.
You cannot start your serve inside of the court. If you have concerns about another player starting their serve within the court, please mention it to the team playing and be respectful while doing so.
And teammates, be helpful to your server and honest to the other teams.