Can solar panel charging slow down the draining of phone battery?
Your Experimental Setup:


You listed your chargind data as 0.11A@5V, or 0.55W  
Your stated test protocol uses many/all power consuming parts in your phone at high output (in many phones this can reach well over 10W total load)  
You then timed fall time from '100% charged' to '90% charged,' as displayed on your phone's screen to gather test results.


Anticipated Problems for your Experimemt:


Charging at ~0.55W while draining at >10W is a very small 'drop in the bucket' charge rate to be testing, so your error % will be raised and your accuracy &amp; precision of timing &amp; charge state measurement become incredibly demanding.  
Using the on-screen charge-status indication adds 2 major sources of accuracy/precision loss to your results:  


The OSD charge status doesn't update with a very high refresh rate, due to the normal timing of charge/discharge the refresh rate of this indicator could be several seconds long  
The OSD charge status indicator on the vast majority of phones relies on a 'fuel guage' circuit to guess about the battery's state-of-charge. This is usually accomplished by measuring total input/output current, then compared against past 'learning' measurements to 'fill in' data which is not directly measurable in the small increments displayed. Due to this, an error factor lf at least +/-5% should be considered highly possible for the OSD state-of-charge.



Recommended improvements:


Find a lower-drain (but still as steady/predictable as possible) method for your test discharge rate to increase your SNR and allow easjer gathering of meaningful results (maybe open a GPS nav app, with location enabled, power save disabled, and screen brightness as 25%)  
Run your test for long enough that the 'gas guage' ic can give more meaningful output by passing a few of its 'threshold voltages' which it can actually measure, rather than only estimating (I'd recommend staring testing as soon as 'your phone is done charging' is registered on-screen, then run until &lt;=25% charge remaining)  
To be a scientific test, the results must be repeatable, so running this test 3-4 times (both with and without the PV charger attached) can help "weed out" inaccurate results that can be caused by variables (phone ringing, GPS signal fluctuations, clouds, etc.) you can't easily control.