Just a Heartbeat Away?
To Become Acting Speaker of Your House for a Day, you simply have to declare this fact.
If someone else in your house does the same, you will need to take a vote on it. Hopefully, you have an odd number of people in your house.
What are the duties of the Speaker of Your House? Whatever you want them to be. The most logical task would be to answer all incoming phone calls, no matter whose phone rings.
Is it still proper to say that a (cell) phone rings? Do younger people even know what a pre-cell phone ring sounds like?
Since you will be Speaker of Your House only for a day, make good use of your time. Execute your duties as often as possible, whatever those duties are.
If you, as designated or voted in Speaker of Your House, are unable to fulfill your duties of the day for any reason, another Speaker will be designated or the runner-up on the ballot will take over for you.
You probably don't want that to happen.