The key here is copyright on the name "Phaser" from the authors of the upcoming Star Trek series, at least that's what I remembered from a blog post some time ago. I'd try to contact them directly and ask if they have any problem with using the name. You can stick to the current name and if they force you to do so, then do it only then.
I was waiting for Lazer because I thought the decision was final, but if you're still considering it I'd say stick to Phaser. The difference internally it not a big problem - if it's a next version number it speaks for itself that you just can't include it in your old project and hope it'll make you fix a few lines and that's it. It would only mean you'd have to specify the version in which you're writing a tutorial, but it's a common sense to do it anyway.
There's a huge collection of materials about Phaser already, the gamedev community and the whole world got used to it, the framework is recognized as one of the best out there even from non-developers, and it would be a shame to waste such marketing recognition and start with something totally new. On the other hand you as the author is a recognizable figure and if you change the name to Lazer it will take some time to clear the confusion, but people will accept it and move on.