Two-thirds of podcast listening is done on smartphones and other mobile devices according to Edison Research’s latest data. So a new forecast that the number of smartphones in use will grow at a slower clip—including iPhone users that are still critical for podcast consumption—means podcasts will need to convert more current users than rely on new adopters.

Smartphones are now widely in use so it’s not all that surprising to see eMarketer’s latest forecast to say the U.S. smartphone market has been experiencing slower sales growth. “We forecast that the number of smartphone users will grow just 3% in 2019,” it says a report released Monday. A big reason for that is smartphone prices have topped $1,300 and so customer are opting to keep their devices longer, rather than upgrade for new phones with new features that are seen by many as optional. Yoram Wurmser, an analyst at eMarketer, said instead of getting a new phone every 18 months most people are now using the same phone for three years.

Yet while sales are slowing, the number of U.S. smartphone users is substantial. The eMarketer team pegs the current user base at 232.8 million and it predicts that number will top 250 million within the next five years.

With a majority of podcast listening still on iOS devices, it’s what is happening with iPhone sales specifically that is most eye-opening for podcasters. In the first quarter Apple reported iPhone sales declined 18.4% year-over-year and, based on the trends it’s seeing, eMarketer expects Apple’s revenue to come more from sales of wearables like the Apple Watch and home accessories like the HomePod.

More smart speakers could benefit podcasters. Edison Research’s Infinite Dial 2019 report said 10% of monthly podcast listeners aged 12 and older already consume shows on a smart speaker. And one-in-four listen on computer or laptop.