Your phone is used for navigation (GPS, maps) and capturing your journey (photos, videos). In order to manage longer sections in the wilderness with sufficient power find a few important tips here.
Keep your phone in flight mode to save significant battery. Battery savings mode is not recommended as it will delay GPS fix while navigating and geo-tagging of photos is not ensured.
Switch off your phone during night rest and keep your phone warm (close to your body) to avoid draining of the battery in cold weather.
Using the OnePlus 6 as a reference phone which has a 3300 mhA battery.
The dash charger of the OnePlus 6 charges the phone to 90% in 30 minutes which allows you to recharge during a lunch break in a village.
A fully charged battery and phone switched to flight mode will last between 1 to 2 days depending on usage (navigation, photos, videos).
Carry an extra 10.000 mhA power bank to add another 2-4 days of power.
Additionally for longer hiking sections you can carry a solar panel. Shown here is a 21 Watts panel which charges the phone in approx 3 hours under full sun light. This gives unlimited power supply