Moving an Eir pole and line

Firstly, it's Eir's line. They can move it and probably will advise you in due course.

You rent a service from Eir, how they get it to you is up to their network distribution planning. Your neighbour will not be doing any moving or technical adjustment to the phone line infrastructure.

Eir on the other hand have many and various arrangements made with public and private organisations outside of your property to do that. They don't have to ask your permission to work on their own network. The physical line your service is carried on, is their property and can take any route they deem appropriate to get to you. Your 'line' could be moved and re-routed anytime and anywhere between your physical property boundary and whatever route is necessary to make a switching network connection at your nearest telephone exchange.

What impact do you think it will have on you?

If sight lines are to be compromised with the repositioning of the pole then that is something I think you should bring to the attention of both the roads section of your local Council and the engineering branch of Eir. You need to be sure though that this the case as there are set dimensions for vision line splays.

I honestly can't see this having any reduction on internet speed.

Your service/speed won't be affected. Eir will consider sight lines. I honestly don't see what has you do peeved. Contact Eir if you have any concerns but they are perfectly entitled to move their networks if they wish.