There's too much stuff in your cockpit. Get rid of either the map-bag or the phone, or both - they're just distractions, and when you need to look at them, you should be stopped anyway.
Get rid of the extra brake levers, they're pretty pointless, since you have very little stability (high CoG combined with narrow stance) when using them - that's just dangerous - when you're not certain of conditions, always ride the hoods or better yet the drops, so you can brake safely and in a controlled manner.
That done, mount a bell on any of the freed-up real estate. I've got mine on the right inboard position, which isn't ideal, but you should be ringing the bell at least 8 seconds before intersect, so plenty of time to switch back down to the drops and be prepared to come to a full stop.
My credentials: I've commuted and toured on a race bike for around 2 years. Due to local regulations, the bike originally shipped including a bell, but I think I had to mount it myself.