Review a mobile UI screen for one-handed thumb reach before it ships

Review this mobile screen specifically for one-handed thumb use. Most mobile UX reviews default to generic "mobile-friendliness" commentary about font sizes and tap targets; I need something narrower and more useful: where does this layout actively fight a user holding the phone in one hand and reaching with their thumb.

SCREEN LAYOUT
Top nav bar with back arrow and settings icon. Middle: scrolling list of saved cards. Bottom-right floating '+ Add card' button. Delete icon appears top-left on swipe.

DEVICE SIZES IN SCOPE
iPhone SE (smallest) through iPhone 15 Pro Max (largest).

PRIMARY ACTION ON THIS SCREEN
Add a new saved payment card.

EXPECTED USE CONTEXT
Standing in a checkout line, phone in one hand, other hand holding groceries.

PHASE 1 — MAP THE SCREEN TO REACH ZONES
Divide the screen into natural, stretch, and unreachable zones for a right-handed thumb on the smallest device size in scope, then note whether the same map holds or shifts for the largest device size. Place every interactive element mentioned in the layout into one of these zones.

PHASE 2 — FLAG REACH CONFLICTS
Identify every case where the primary action sits in a stretch or unreachable zone, and every case where a destructive or hard-to-undo action (delete, remove, cancel-subscription) sits in the natural zone where an accidental thumb tap is most likely. These two conflicts matter more than any other mobile issue on this screen — surface them first.

PHASE 3 — SECONDARY MOBILE ISSUES
Only after phase 2, note anything else mobile-specific worth flagging (tap target sizing below the ~44px comfortable minimum, elements too close together for a thumb to hit reliably). Do not restate desktop-style critique here.

WHAT NOT TO DO
Do not produce a generic mobile checklist unrelated to thumb reach. Do not assume left-handed use unless told to — state clearly that the reach map assumes right-handed use and that a left-handed user mirrors it.

OUTPUT FORMAT
A short reach-zone map (natural / stretch / unreachable, with elements listed under each), then a numbered list of reach conflicts in priority order, then a short secondary-issues list. End with one line stating what would change if you also had to design for left-handed use.