Same experience as acer5050.
Planted 3 or 4 'Becky Towe', in our garden: longest lasting was about four years.
Have one (variegated-leaf) 'Harlequin' that has, so far, done no more than linger for about four years.
Have planted a number of dozen 'Nora Leigh', in gardens I planted and maintained, including about a dozen in our own garden.
May have lost one or two, in total, over years (some over more than ten years).
The flowers of 'Nora Leigh' may not be that showy, but find that the foliage looks good, late in our growing season. It's quite late flowering for a tall garden phlox cultivar, at least here. Have wondered whether it's powdery mildew resistance may be related to that.
Re tall garden phlox maintenance: I do pay attention to keeping an air flow around the plants, to watering, to upgrading soil periodically and to taking out any powdery mildew infected parts , when seen, but I'd say, of several dozen different tall garden phlox cultivars that I've planted and maintained, 'Nora Leigh' is among the best. I, especially love the way it carries it's variegated foliage into the Fall, when colour in a mixed perennial bed may be getting sparse.
Forgot to mention 'Shockwave' (also variegated leaf). Definitely not as large and robust a plant as 'Nora Leigh', at least in our growing conditions: Had five: Longest lasting, about five years.
