How to make your own electroluminescent wire?
This is not going to be the answer you were hoping for, unfortunately.  

The term 'phosphor' refers to any material that exhibits some form of luminescence.  The key word there is some form.  There are many varieties, and specific phosphors exhibit a specific kind of luminescence. 

They cannot be used interchangeably.  Your neon tube phosphors are fluorescent, which means they will emit light of a different frequency (color) if the right light source is shined on it.  In other words, and I am sure you're very familiar with this, argon and mercury vapor produces ultraviolet light, which hits the phosphor coating, causing the phosphor to glow in one of hundreds of possible colors available in neon lightning.

That is the only way those phosphors can be made to emit light.  They are fluorescent and nothing else.  They are not phosphorescent (continues to glow after the light source is removed), nor are they chemiluminescent.  And, sadly, they are certainly not electroluminescent.  

In other words, all of your neon sign phosphors are completely useless in the context of EL wire.  None of them can be made to emit light via electroluminescence.  Sorry. 

You can only make EL wire with electroluminescent phosphors, which are all semiconducting.  And there is a grand total of 3 that are of any practical use (i.e., not so horribly inefficient that producing usable amounts of light would quickly overheat the display) for EL lighting. 

Those three electroluminescent phosphors are all zinc sulfide, doped with either copper (greenish), silver (blue), or manganese (yellow-orange).  Those are the only 3 things you can use.  Because those are specifically electroluminescent.  Electroluminescence is a fairly rare property.

However, there is a different way your phosphors can be (and probably already are) used with EL wire. 

The different colors in EL wire are done in exactly the same way as your neon lamps, albeit with a different light source. Blue-green light emitted by the EL phosphor core of the wire, which makes a fluorescent dye in an outer PVC jacket around the wire fluoresce a specific and different color.  So, while you must use zinc sulfide doped with copper, silver or manganese to produce the light, you can certainly do whatever you wish with this light once it is emitted.  If you have neon phosphors that respond well to blue or green light, then you can definitely use them as a coating for the EL wire, though it will need to be added as part of the PVC manufacturing process to make anything remotely robust.  Soda paste won't cut it, as it is on the outside, instead of coating the inside of a glass tube.  And it must be flexible.  

I would wager that some (if not all) of the fluorescent phosphors used in the PVC jackets around EL wire are in fact the exact phosphors you use to make those same colors in neon lamps.  Only mixed in with clear plastic, rather than coating the inside of a glass tube.

It might be worth using a neon tube with EL wire inside instead of gas, and using that wire as the light source for the phosphor, only painted inside the tube like any other neon light.  It would be dim unless you used a bundle of EL wires, but could produce a cool effect.

I know that is not what you were imagining or hoping, but thats the cards physics has given us, sadly.