I think it's a Salvia, though I am not sure which one - even though I have one in the garden! Someone will know. Could be Salvia farinacea.

if it is shrubby I'd go for perhaps Buddleia alternifolia, if it is its a nice shrub and not as thuggish as the B davidii types.

How long has it been in the garden?

any chance of a close up of the flowers.

I thought Buddleia too...but could it be a Russian Sage? Perhaps not...a bit too 'droopy' for that.

If it was a Salvia, the stems would be square . . .

It looks to me like a variety of Mexican Bush Sage (Salvia leucantha). Even more so if the flower spikes are softly fuzzy--it makes a great "five senses" garden plant.