Is Phnom Penh safe for travellers?
Phnom Penh is manageable, but it asks for more city sense than Siem Reap. Keep bags and phones boring, use sensible transport at night, and do not let a tired arrival become the moment you improvise.
Answer
Most travellers do not need to fear Phnom Penh, but they do need to pay attention in the predictable moments: arrival transfers, phone use near traffic, late-night movement, riverside/tourist areas and quick decisions made with luggage in hand. The city is not defined by danger, but it is less forgiving than a slow temple town. Use reputable transport, keep valuables uninteresting and build a little margin into evenings. Safety here is less dramatic than disciplined.
Recheck before you go
Conditions can change. Check current official advice before you travel.