Are there pockets for inserting knee pads?

The Real Answer: Not exactly. 9" above the bottom of the front, outside hem, below the knee, is a 2 3/4 inch slot that acts as an opening to a "pocket" above it. I was able to roll and stuff a 511 knee pad into each leg. Fits perfectly. However, it does not function properly at this height on my 34" length Riggs. The 511 pad pockets are positioned exactly 12" from the bottom of the pants (hem) to the bottom of the pad pocket seam. These 3 inches make all the difference. Unlike the 511's, if I fall or kneel with the (now) padded Riggs, it comes short and offers insufficient protection. When kneeling, if I don't manually hike up each pant leg, my results are poor. So, in a fall or a tactical/hunting/photography situation where one might need to drop quickly (presumably when hands are occupied) chances are you won't get enough pad. With the 511's, your knees will be protected if you want to drop suddenly or if you stumble in rugged terrain. Still, better than nothing. I generally prefer the Riggs over 511. They are more rugged and the 511's water resistance doesn't last long. (I think the 511's are thinner, therefore cooler in warm/hot conditions. They are also very tough.) Riggs needs to re-design the Ranger with the "pad pocket" 3 inches higher.

Will the side pockets on the thigh fit an iPhone 6S Plus comfortably?

Both cargo pockets and the left top pocket fit big phones. I carry two phones daily for work. My Note 7 fits good with slim case in top front left pocket. My Droid Turbo 2 in a bigger rugged case fits easily in either cargo pocket. I leave the back snap fastened and the front unsnapped so is easy to grab in a hurry but not likely to fall out while sitting in a chair or car seat

Are these pants gusseted?

Yes, the pants have a gusseted crotch

Do they run true to size?

I purchased a 34/30 pair from a local store and am wearing them right now, for the first time and haven'twashed them yet. I normally wear a 33/30. These in 32/30 were too tight and 34/30 is too loose so I'd have to say the ones from the store would be about true to size. I feel like they are a little losse for a 34/30 so I hope they shrink a little. I'd rather we r have a bit loose than so tight they give me wedgies. Besides looser are cooler in the summer.