Let's calculate the miles Phillipa rode each day.
Friday: \[ \text{Miles on Friday} = \frac{(13.5 + 8.5)}{2} \] \[ = \frac{22}{2} \] \[ = 11 \text{ miles} \]
Saturday: \[ \text{Miles on Saturday} = 18 - (2 \times 4) \] \[ = 18 - 8 \] \[ = 10 \text{ miles} \]
Sunday: \[ \text{Miles on Sunday} = 20 - (5 - 3) \] \[ = 20 - 2 \] \[ = 18 \text{ miles} \]
Now we compare the miles ridden each day:
- Friday: 11 miles
- Saturday: 10 miles
- Sunday: 18 miles
The maximum distance is on Sunday.
Therefore, Phillipa rode her bicycle the most on Sunday.