function getPhis() {
	/* eslint-disable no-invalid-this */
	var Phi;
	var val;
	var k;
	var w;

	Phi = matrix( [ this.K, this.W ] );
	for ( k = 0; k < this.K; k++ ) {
		for ( w = 0; w < this.W; w++ ) {
			val = ( this.nw.get( w, k ) + this.beta ) /
				( this.nwSum[ k ] + ( this.W*this.beta ) );
			Phi.set( k, w, val );
		}
	}
	return Phi;
}
Get the phi matrix. Each row is a topic distribution over words.

@private
@returns {Matrix} phi parameter matrix