TL;DR
Short answer, yes. Long answer, it's going to take a lot of work. Alternate answer, just make a shake charger.
Eel Power
According to Wikipedia, electric eels (which aren't actually eels) produce 100-860 V at 1 A for about 2 ms, so between 0.2 and 1.72 J of energy. This is for burst damage mode. The article says they can perform these bursts intermittently for up to an hour, but doesn't say how often, so it's hard to get total energy produced. In fact, I can't find any source off-hand that gives me this value. Either way, it's probably not a huge amount of energy total.
They can also use a couple different organs for electrolocation. In this mode, they output around 10 V at 25 Hz, up to several hundred Hz. Unfortunately, Wikipedia doesn't give amperage, so we can't calculate power or energy. My guess is it's a lot less than 1 A.
From this random Reddit question, a cell phone holds about 18 kJ of energy when fully charged. This random Android forum thread says a typical phone lasts 5-10 hours, or 300-600 minutes, while actually using it. So 60-30 J per minute. Let's assume you need about 1 minute to relay critical information to the 911 (999/whatever) operator. Let's also assume the latest iPhone is a bit more efficient than the Androids in the above thread (from 2012), and is setup for low-power mode, and further assume that lets it run for 15 J per minute.
Our first assumption might be to use the 1.72 J eel shock times 9 to get 15.5 J and charge the phone. But that's at 860 V, which is far higher than your wall charger is intended to use. If you find a small eel (around 10 cm says some Yahoo answer I found but can't re-find), the 100 V should be in the right approximate range, so you need 75 eels.
It shouldn't be hard to find some electrical wire you can use to transfer energy from the eel to the charger, but you have a couple problems. First, your wall charger is expecting an AC input, not DC. It's hypothetically possible to overcome this with applied science, but I'm not sure exactly how off-hand.
Second, you need to know which end of the eel is positive, and which is negative. With a proper converter (ideally, just replace the entire wall charger with a variable-input converter from 100-900 VDC input to 5 VDC output), it won't matter which end is positive, because the diodes will force the current to go the right way.
This random DC-DC converter takes an input of 30-800 V and outputs 24 V, so it's definitely possible. From there, you can find about 37.9 trillion types of 7-35 V input, 5 V output DC-DC regulators. Combine the two and you have an electric eel iPhone charger. I'm fairly confident you can find both of those devices on any reasonably large aircraft without even building it yourself.
Of course, the eel isn't going to cooperate, so you probably won't get the full charge each time, so you might use 200 eels or something just to be safe (even at full charge, 200 of the most powerful eels is only 116 J). If you can get them to repeatedly burst, you could use fewer total eels (just count each burst as one eel).
Shake it, Baby
At the end of the day, I'd think an entire airplane worth of salvage would make it a lot easier to do this:
Source: Instructable
A comment on that instructable says:
Shaking the finished assembly [note, this guy's "assembly" isn't identical to the instructable's instructions] gave me 7.4 volts. I tried recharging my phone and it gave 33% charge after rigorous shaking for 15 minutes.
It's 4 diodes, any random tube of about the right size, and some magnets. The hardest part is coiling all that wire around the tube. That sounds a lot nicer than trying to hack together an electric eel charger. (Of note, there's a bit of contention in the comments saying that specific design sucks and may not actually work, while others say it works fine. It's just the first one I Googled, but regardless, real designs aren't very complex, especially for a one-off phone call.)
