Do not consume the souls of the bosses, you'll need them to get access to some unique weapons and spells ;)
Here is the list of what each soul does: http://demonssouls.wikidot.com/bosses
Also, Tower Knight is a major difficulty jump from Phalanx. My tip is to first rush past him and finish off all of the Archers on both towers before confronting him. After doing that, rush back to him, and always keep to his back, hitting his legs until he falls down. The trick is to always be on the look out, never hitting him more than once, or twice if you're feeling bold.
If you're a Ranged/Magic user, you can snipe at him from each of the sides, as his only ranged attack, the Lance throw, is pretty easy to see and dodge ;)
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
