Besides owning your own car or scooter, there are a number of ways to get around in Phnom Penh, all with inherent pros and cons.
You can walk: you'll arrive looking like a hot mess (literally) but it's a great way to take in the varied smells, sounds and sights of the city as well as become better acquainted with the layout.
You can ride a bicycle: again, you'll arrive looking like a hot mess with helmet plastered hair but the landscape is very flat so it's not a very strenuous ride. At least, unless you land up on a bustling street during morning rush hour and have to dodge piles of fruit and vegetables, fresh produce sellers, dogs and rumbling trucks.
You can take a tuk tuk, which can get expensive if used frequently but is an enjoyable way to get around, especially when the owner has kitted it out with flashing lights and tinny music.
You can take a cyclo which is similar to a rickshaw but is a chair attached to the front of an elevated bicycle. A number of guidebooks and people will suggest it as a slower means to get around, allowing for picture taking. i however haven't ridden in one yet, mostly 'cos I feel I little uncomfortable about someone having to exert so much energy to get me around.
You can take a motodop, i.e. a scooter, which is what I use quite a bit. It's cheaper than a tuk tuk and I thoroughly enjoy the experience of whizzing around (actually not whizzing, they go quite slowly) town. In my experience, the drivers are great and most of the time know the place I'm asking them to take me to.
A problem I have encountered on a few occassions is a driver saying yes to my request and en route realising he has no idea where the place is, which has resulted in a few comical situations involving an exhange of apologies( "Sorry!!! Somtooh!" on repeat), stopping frequently to ask strangers for help and much broken Khmer from my side and broken English from his.
There are always a number of drivers wanting to transport you from the moment you step out your front door. I don't really mind who I go with, as I said they're mostly great. There is one driver who I now try to avoid though, with limited success. He has one eye, which makes me a little doubtful of his depth perception, a key skill in busy traffic. After getting horribly lost with him and learning of his poor track record in finding places, I vowed to avoid him.
Last Sunday I stepped outside, planning on visiting a church quite far away. I was already running a bit late and waved over the first driver I saw. With a sinking heart I realised it was the one eyed man who'd tricked me with his eager wave and cap partially obscuring his face. As there were no other drivers in sight I resignedly asked him if he knew where a school called called Northbridge was, as the church was near there. He confidently repeated my question and nodded vigorously. So off we went. When he took a left turn I thought, "I'm pretty sure it's straight but maybe he knows a shortcut." When he took another turn in the opposite direction thought, I started laughing and thought, a little desperately, "I think we're lost but he seems really confident, maybe it's a different route." He drove up to Hope School (nowhere near Northbridge) and the conversation that followed went like this:
One Eyed Moto Man (with a flourish of his arm and great pride in his voice): Northbridge!
Me: No, no, not Northbridge, Hope.
OEMM: (another flourish): Northbridge!
Me: No, I want to go to Northbridge.. uh.. Knom (I) uh.... tiw (go) uh... Northbridge.
Needless to say I never made it to church and arrived back where I started a few minutes later, to the great amusement of the security guard!