Why doesn't pug mixin work with svg?

Question

HTML

I use this
mixin mixin icon(name)
svg(class="icon icon-#{name}")
use(xlink:href="img/svg-sprite.svg##{name}")
tried this
mixin icon( name)
svg(class="icon icon-" +name)
use(xlink:href="img/svg-sprite.svg#" + name)
call
+icon(phone)
substitutes NaN for name

Answer 1

Is there a phone variable? you either pass a string
or a variable
+icon(phone)