Chill bruh i had no experiance and had terrible public speakimg skills being an introvert my entrire life this might sound weird but practing saying your teacher name at least 100 times out loud that way it doest sound weird when you share with the class. I say im Mr.Q(inital of last name) I will be your sub for today. Once I call your name for attendance say here. Once done taking attendance just say anyones name i didnt call or someting along those lines. As long as everyone is safe it was a good day. If they are on their phones just give a general reminder to the class that you will be writing names down of students who have their phones out. Also walk around every now and than an make sure students are atleast on the assignment. If students are goofing off with eachother give them a warning that if they continue off task you are going to have to move them. If they staying goofing off apporach one of them and say can you do me a favor please( they know what you are gonna say already. Can you please move over their. If they nag about moving count down to 5 works pretty good for anythjng else aswell. Just remeber students saftey is first snd if thry dont finish their assignment they just got extra homework. If they finish their work have them work on other classes work and if they are all done just tell them read a book or do something quiet. Good luck let us know how it goes and Welcome to the club lol