Fenix is a bruiser with ranged attacks, which means he doesn't play like other bruisers or other ranged heroes. He deals quite a mix of sustained and burst damage, and his health pool is higher than assassins but on the low end of other warriors. His basic attacks are quite slow and have a delay but deal decent damage making each shot count. The lack of self-sustain or hard cc severely gimps his solo tanking potential and he's somewhat slower-paced, but his abilities are quite powerful regardless and he can stay out of troublesome situations really well. He fits into teams as a safe bruiser or a low-cc tank, or can also be a strong peeler for a squishy backline against heavy divers.
Deploy seems a little funky at first, but what it does is basically give you an offensive Abathur Deep tunnel every time you die or Hearth, at the cost of not being able to use it on the field. It's an extremely powerful tool that allows instant reinforcement, and even better, you still have access to a cool mount! The Shuttle doesn't let you have cool custom mounts, but what it does have it the ability to prevent you from being dismounted for silly reasons like going through a minion wave, and also gives you a pretty strong shield. You can still be hooked and the such though, and it comes at the price of being a little slower on the upkeep since you can't use abilities immediately coming out of it. Still, the ability is very powerful and thematic.
Scarabs are a nice utility tool that provides a little bit of mobility and damage but the most useful aspect is the knockback. The daze is mostly great simply for the disengage, but there will certainly be situations where it's more optimal to charge face-first into an enemy, or maybe just use the pulse to stop a channel. Singularity Charge allows you to move and shoot, which is a lifesaver due to how long it takes to actually fire and can let you kite pretty well, and the shield damage can be a great boost against anti-sustain heroes like Tassadar and Chen. It doesn't last super long and has a pretty long cooldown, so make sure to cancel it if you don't need it. Heart of a Zealot makes you super slippery, letting you instantly get out of sucky situations with a potent self-cleanse, and using it when the enemy tries to pin you down can save your life. It won't save you from damage nor stasis effects like Cocoon, but it can stop you from getting shredded by chainstuns and letting you Disruption away.
Guardian Shield is a supporting ability that gives everyone around you armor, except it doesn't count as armor. 25% damage reduction for your whole team on call is pretty good, and it has a small mana cost and can be toggled on and off with a small cooldown, but it's not a passive ability like arthas' Frozen Wastes. It can very easily kill you if they all get hit by AoE abilities, and although you are probably tankier than your allies you still don't want to be countered by the enemy just picking you off, so choose this heroic if you're less likely to get focused or you really need to defend your allies.
Reconstruction is literally a resurrection on a 60 second cooldown, and is another way to instantly reinforce your allies during a fight, and since the enemy will likely try and burn through your second health bar to prevent the revive you're basically a nice big distraction for the enemy team to waste their time on. Of course, if you do manage to revive you're a nice big problem for the enemy team to deal with. The downside is that the revive takes 3 seconds which is likely enough for the enemy to either kill you off or just wipe out your teammates, and if your whole team dies and you're the only one left alive the enemy team can pick you off with impunity. Being able to activate it is okay because it can be used as a 3-second full heal or as a way to cleverly avoid burst (or to just kill yourself...?) but the real value comes from the resurrection, so unless you expect to get focused it's not as strong.