A selected-app blocker makes sense when the rest of your iPhone is useful, but a few installed apps have become too easy to open. Instead of restricting the whole phone on a schedule, you choose the specific distractions and leave practical apps outside the block.
Fella is built around that model. It keeps the distracting iPhone apps you select blocked by default. Apps you do not select can remain available, so calls, texts, maps, work tools, and other essentials are not part of the boundary unless you choose them.
There is a defined exception for a genuine need. Each Fella blocking session has one five-minute emergency unlock. Use it for a specific message, code, link, account task, or other real reason inside a blocked app. When the five minutes end, the selected apps lock again automatically.
That is intentionally different from a schedule. If you know you need an app at a certain time every day, Downtime or another schedule-based approach may be more natural. If the problem is that the app is open whenever boredom, a transition, or a difficult task appears, a default block can be the clearer boundary.