I'm making a Shaman in 4th edition and I'm trying to make him be one with the spirits. I was wondering if a shaman can have 2 spirit companions. It would be cool if I had a Phoenix as one spirit companion and a Thunderbird as the second. Are there any feats or bonuses that allow it, or would it be up to the DM to have me do a quest for it?
Ok, the answers to this question are basically:
Let's start with the basics. Under normal circumstances you get one spirit companion. The power is worded in such a way that it only allows you to call your companion if you don't already have it in play.
However, certain powers, for instance the daily utility power Spirit Summons allow you to have multiple spirit companions out during an encounter.
Lastly, you're basically free to flavor your spirit companion however you want to. If you want it to be a Phoenix on one summons and a Thunderbird on another and characterize them differently based on which one appears (or summon different ones based on the circumstances) that would likely be a welcome bit of roleplaying. It wouldn't really have any mechanical effect, but it would certainly be an interesting class feature.
To sum up. Normal rules allow you to only have a single spirit companion at a time, but as with most rules, there are exceptions though it appears that's the only one. If you want to have two spirit companions you'll have to wait until L10 and even then it's restricted to once per day. That said, nothing is stopping you from having both these animals as your spirit companions, provided that only one is out at a time.
The Shaman's Spirit Companion's precise nature and appearance is explicitly left ambiguous to allow players to role play all sorts of possible spiritual manifestations, including multiple different companions.
It always helps to back things up with a print source, so here's an excerpt from Primal Power, page 60, where the Spirit Companion is described:
Although this example uses a random rotation, it isn't necessary to depict it as such. You could select which companion to summon at any given moment. You could even have multiple spirit companions simultaneously purely for story reasons.
For example, I played a Shaman with three spirit compansions: a bear that could be seen and would fight (the actual token that went on the map, the official, by the rules, spirit companion), a hawk that kept watch (and, storywise, provided the benefit for Spirit's Wisdom), and a squirrel that healed (and, storywise, provided the benefit of Healing Spirit).
As long as you don't violate the rules (eg: you cannot use Call Spirit Companion to summon two companions onto the map simultaneously unless the rules specify otherwise) you can come up with any story you like... provided, of course, the DM and other players accept and want to role-play with it!
In your specific case, you could describe having both a Phoenix and a Thunderbird, but only one is fighting at any given moment. Perhaps you can only call one onto the field at a time. Or, perhaps you can role-play as if both are there, but only one is represented by a token, and when you move the spirit companion, you could describe one flying up and away and the other flying down into that new position. Be creative, within the framework of the rules!
Keen Eagle Allows you to summon a second spirit after you action point.
While it's not fantastic, it'll certainly continue the basis of "multiple companions" for your character:
On a more pragmatic note though, if you take Fae Beast tamer, you can get a second "animal companion" through its feature to compliment your spirit companion. You could also grab Wild Talent Master for Sensing Eye and Telekinetic Grasp and reflavour the output of your wild talent powers to come from "a weaker spirit." So you have multiple "spirits" around that do different things for you.
On a "This is unwise, do as I say and not as I did" note, you could instead take the protector druid class (which gives you a pet), the fae beast tamer theme (which gives you another pet), and the shaman multiclass (which gives you a pet...) This will result in 15 minute turns and having dice thrown at you.