Frequency of dominant phenotype (Hardy-Weinberg)
p = p(a) = 0.6

q = p(A) = 0.4

Frequency of homozygous recessive, aa = p2 = 0.36

All other genotypes have dominant phenotype therefore the frequency of the dominant phenotype is 1-0.36 = 0.64

(Frequency of homozygous AA = q2 = 0.16

Frequency of heterozygous Aa = 2pq = 0.48)

And if you want a deeper explanation you really should study this answer by Remi.b