The shows viewership has been on a steady decline but Disney still loves this show. Viewership is less then what is needed to be counted on almost a weekly bases now, so less then a quarter of a million.
There will be a Phineas and Ferb / Milo Murphy crossover in 2018.
It is uncertain how long Disney will support a show that isn't bringing in ratings now. They put a good chunk of money on this series. Not nearly the draw that P&F had.