At this time, Byzantium is pretty much at its greatest capacity to absorb damage - consider that Phocas would have probably made a rather decent Emperor, and if he did win the battle, Basil II would probably end up being deposed. Given that the two were about to settle their differences in personal combat, there is a good chance Basil could have been killed as well.
I doubt there would be much of a difference in Byzantium in the next few decades - after all, Phocas was a rather capable general, and had enough resources at hand to do away with the Bulgarians if he wanted to do this, which I believe he could have at least tried. More importantly, Phocas had at least two sons, Leo and Nicholas. This means no succession crisis and numerous husbands of Zoe as in OTL, but perhaps one of Phocas's sons can be married to either Anna (Basil's sister), or one of Constantine VIIIth's daughters, thus increasing their legitimacy.
The most important effects would be in Russia. No Varangian mercenaries probably means no alliance between Vladimir and Basil, no marriage of Vladimir to Anna, and no baptism of the Rus. At the very least, this may either delay the baptism of Rus by a few decades, or make the Rus go with the Catholic rite, if the Byzantines do something that would alienate Vladimir. A far fetched possibility would be Muslim Rus, although quite a bit would need to be changed about the geopolitical situation of the time to allow for that.
