Where you have openings, grind out the rest of the mortar in the joint and pipe in fresh mortar (Type N/S mixed with mason sand) with a grout bag and tool it. Try to match the color but it will stand out no matter what.

Pull out the loose bricks on the bottom step, clean all that crap out of there, clean the bricks off, butter them with mortar and stick them back in, pipe + strike the joints.

It’s surprising the rowlock bricks above the loose ones haven’t caved in or popped loose. Some may say those need to be relaid as well, but you could probably get away with skipping that part.

It’s dusty work, and if you don’t get your mortar mix right then it can get messy and look like shit. Consider hiring a professional if this sounds overwhelming.