The following makes a bug far quicker to fix:
A notification didn't arrive. There are two switches, and both have to be on. First, iOS Settings › Notifications › Phase must allow notifications. Second, each note has its own notification toggle on its detail screen (Settings › the note). A note you added yourself starts with its notification switched off.
Two notes overlap. Which one shows? The one you added first. The list in Settings is sorted by start time for readability, but the note that wins is the earlier one in the order you created them. Overlapping notes are marked with an "Overlap" badge so you can find them.
Phase collects nothing and never sends what you write to us or to anyone else — the only network traffic is the App Store handling its one-time purchase. The details, including how to delete your data, are in the privacy policy.