Is a phone app worth it?

I have had a SAAS idea that I've imagined as a website, but I've recently wondered if also offering it as a phone app would get more people to use it. But seeing the phone app distributors taking 15-30% of the income, I don't know what to do. Is there a way around it? Is it worth having users subscribe through the phone? I was thinking of having a $5 subscription.