He is quite the charmer! I've never personally dealt with separation anxiety, but I have heard two opposite ideas:
One is the idea you mentioned--change your schedule, your routine, etc., so that the dog can't start anticipating when you'll be gone, although I'm not sure if that is for severe separation anxiety or just a dog that gets a little sad when you leave (and they all get a little sad when you leave!).
I've also heard that you should try doing things exactly the same, so that in the long run, Axel will know you're leaving, but will equate your leaving with you always coming back. So, for example, at first you would put him in his crate, grab your purse and your keys and head towards the door, but don't touch it or go out. Then come back and put your things away, let him out, ignore for just a little bit (it helps him understand that leaving and coming home are not big. exciting. events.). Once he's calmly just sort of standing there, you can pet and love and play, etc. He will hopefully begin understanding that you're not leaving forever. Since you say he only gets upset when you walk out the door, this step should be smooth. Then you can start upping the ante by touching the doorknob, then opening the door but not walking out, then walking out the door and coming right back in, and then start being "gone" for longer and longer amounts of time (starting with very short amounts of time like 1 minute). But make sure to keep the leaving process the same. Some dogs really really like to have schedule or order to this kind of thing--to the dog, if the way you leave is always the same, then it follows that everything will always be the same in this situation, and you ALWAYS come back, so...
From what I understand (this is from a colleague whose dog had separation anxiety), this is a very long process for a dog that's already developed the anxiety, but it's not totally impossible. Try not to move through the steps too quickly, but if you find that he's not taking to one step very well, back up and build up to it again. Apparently the first time she stepped outside the door, he pretty much had a panic attack. So she backed up and worked on just opening and closing the door for a few more days. She wouldn't come back inside until he had stopped barking/crying--sometimes this was literally just as the dog was catching its breath to start again, but she held her ground.
Axel still seems young, so hopefully it will go better for him that my colleague's fully grown dog (adopted from the shelter)--it took her 2-3 months to build up to being gone for a workday. This is somewhat similar to the way that I desensitized my boy to being alone for the day, so I think it's probably like starting all over from the beginning, only it takes longer because of the instilled anxiety. Perhaps his original owners never took the time to desensitize their pup to being alone--I took a week off work to make sure Jasper wouldn't develop anxiety, and it's paid off immensely. But I know some people who can't/won't take the time to do so, unfortunately.
Sorry for the long post! I hope this or another post helps just a little bit, and let us know how it's going!
Forgot to mention: My friend was a teacher for a while, and they adopted their dog during the summer when she knew she'd have time to work on this. She did this every day, even though she didn't need to leave. Since Axel is lucky enough to have you home with him a lot, you'll probably have to purposefully practice this throughout the day. But like I said, what a lucky dog to have his people home with him so much!