In my experience as a former technician for a major telecom that had to deal with the wiring in many, many homes, there are three likely configurations of the wiring in your home.
FIrst, and best, is home runs from each room to a structured wiring cabinet (or sometimes just a blank wallplate) somewhere in the home, like so (forgive the quick and dirty diagram):
Green boxes are wall outlets, blue lines are the wires, orange box is where the utilities come in from the street, and red box is the structured wiring cabinet/blank wall plate.
Generally, with this configuration the cabinet/blank plate will be in a closet (often the master bed closet). A good clue you have this configuration is if there are exactly two cat5/coax lines in the box on the outside of the house where the utilities come in, unless you only have two jacks in the entire house (depressingly common to see houses where only the kitchen and master bedroom get wired up, some builders haven't seen fit to update their wiring practices in decades).
Second likely possibility is home runs to the side of the house where the utilities come in from the street, like so:
With this configuration, you'll see a number of wires in that box on the outside where the utilities come in that corresponds with the number of outlets in the house. It's simultaneously nice that at least all your wires terminate in a central location, while garbage that they terminate in what is usually a decidedly suboptimal location.
The third and worst configuration is as follows:
In this configuration, there is a one wire that goes from the utility box to the first outlet in line, where it terminates and another line goes from that outlet to the next outlet in line, and so on until the final outlet. This is referred to as a daisy chain. This sucks for anything but traditional analog telephones, another case of builders not updating their wiring practices in decades.
That terminated cat5 line going through the brushplate was probably used to connect something to that wall outlet somewhere else in the room through the wall... given your description and what looks like an HDMI cable bundled to it, probably the TV or some other bit of A/V gear. Amusing to see what looks like a full fat RJ45 outlet labelled "phone". You'd think electrical contractors in this day and age would at least be aware that cat5 wire isn't just (or very often) used for phones nowadays.
