First of all, I wouldn't advise you such setup unless your phone line is highly perfect as I am not really sure about the noise factor but such set up would be incremental in line attenuation making the sluggish browsing, sort of lagging while making connections to peers in torrent clients or while browsing, possible disconnections while trying to maximize your allowed bandwidth by downloading and browsing simultaneously ...
NOTE: these are my personal experience as I had done such experiment in the past what you're about to... but hey, there's no harm in experimenting right?
I would also advise you to not to use the normal 'dabi' right after the black wire and the splitter after that... if you can joint the wire directly by using solder to make joint as solid as it can be.
For noise, make sure that if the noise is after the set up or before the set up by hooking up your phone directly to the black wire even without the DSL and then making a trial set up configuration like you drew.
If the noise is before the set up then its clear that your line faulty and you know what to do or who to call
if its after the set up then its probably due to a somewhat loose joint or a small thread is the wire the touching the other wire which it should not.
The black wire has two copper wires in it and its generally not labeled for -ive and +ive ... but for the sake of avoiding cross touching of wires just assume one copper end as -ive and the other +ive .. and strictly remember an follow that throughout the set up.
Let me try to draw it for you my suggested version of your set up...
It rather difficult process and requires bit of skill but it will retain maximum signal strenght for 2 phones and a DSL because of soldering... my recommendation.
This is very easy process and will work but the chances of low signal strength and noise will be higher as at every box and splitter, there is a 'touch' connection between male and female jacks. slight movement, vibration or displacement of this wire set up could cause problems sooner or later. not advised but you can try it first as it easy.