This is a little usual as Ada said in regards to the strength of the phobia but this is not the first time I have heard of this. Condoms are going to be the surest thing you could use to minimize any "contact" with semen.
This does not make you weird, unusual, abnormal or anything else you may think and you should certainly not be feeling this way. Its something that is beyond your control, you cannot help it but it does sound like you have quite the understanding partner. To answer your other question yes this is and can be a legit phobia just as anything else can be.
Ada wrote:It's important to be gentle with yourself. If you try this out. Don't beat yourself up about it in any way. You feel the way you feel and that's OK. Pushing just a little against the fear can help your feelings change over time.
In what you decide to do, please always do keep in mind the above. Much luck you.
Tulula.