solve non linear equations using Newton iterative method

My equations are

 x/sqrt(x^2+y^2)  = -1 + 1/1.2 * cos(phi)
 y/sqrt(x^2+y^2) = 1/1.2 * sin(phi)
 arg(diff((x- jy)/sqrt(x^2+y^2)),a) = pi/2 - phi

Where,

x(a) = cos(a) - a*b*sin(a) - 1
y(a) = a*b*cos(a) + sin(a)

Here variables are

 a b phi

References: https://www.dropbox.com/s/3sv4hs5z5jn3mfr/xyz.pdf?dl=0