See, I disagree with this, but I was also a runner. Everything up to 400m was actually considered a sprint, and treated like a sprint, and trained like a sprint. By sprint, I actually mean, all out effort the entire time.
Regardless of how you look at it, the basics are going to be the same.
If you're training for a specific distance, say, 300m, your training should consist of distances somewhat longer than that, and somewhat shorter than that.
On some days, you'll need to be doing some hard work in the 400-600m range, trying to push up that pace. It's going to be slower than your 300m time, simply because you lose speed as the distance increases. This is slightly more aerobic.
Assuming he's also training for the 1.5 mile, he's got some additional aerobic training there, but if not, do some work where you're running a mile or more.
On other days, you'll need to be doing some speed work in the 100-200m range. You want to train yourself to be able to do a full out sprint for as long as you possibly can, and you want these speeds to increase between sessions. Make sure you leave enough days to recover after this.
And then you want to train to bridge the shorter and longer work, and interval work is great for this. E.g, 100-200m sprint/runs with short rests. Not quite as fast as your speed work, not quite as slow as your 300m pace.
An example, numbers simplified for the sake of an example:
Let's say your 300m pace is currently 60 seconds, or 20s per 100m.
Your "longer" days, you would run a few 600m runs, trying to increase that pace. Say 23s per 100, or 1:18 for the 600.
Your "speed" days, you would do a few 200m sprints, and make sure you rest between them. You want these to be fast, so you'll need more than a minutes rest between them if you're pushing them. Aim for something like a 16s pace per 100, or 32s for the 200.
Your "interval" days, you're trying to bridge the speed with the endurance. You want much less rest than your speed days, since you're targeting recovery ability. You can either run your intervals at a faster pace than your 300m pace, and/or at a longer distance than 300m.
You can start with something like 6 sets of 100m at 20s. You'll want to do a minimum of 6 intervals, and if you're doing it right, you'll want to be collapsing about halfway through. The whole point is to tax your recovery ability, where you're not quite ready to run when it's time to start running, and you don't want your speed to degrade.
I would say it's better to get a bunch of "perfect" intervals, where the first couple feel a bit slow, but you hit the pace on every one of them, than to keep getting slower as you go on. Then, next time, drop your target times a bit, and do the same thing. It somewhat defeats the purpose if your intervals look like: 15s, 16s, 18s, 21s, 24s, 26s. Assuming that your 300m pace is 20s per 100: first session, do 6x100 at 22s. Then 21s.
A stopwatch (not a wrist watch) and a track were the way we used to do these. A phone is probably too big, but I dunno, we didn't have those back then. Here and there we had a coach yelling out the seconds, but mostly it was just us with our own stopwatches.
Besides working on just the building blocks... speed, endurance, and intervals... you're also just training yourself so your body knows what a certain pace "feels" like. This is where the stopwatch is really useful/important. You should develop a pretty good intuitive feeling of exactly how fast you're running over time.