\[\phi\left(x\right)\sim-\frac{\pi}{4}+\frac{2}{3}(-x)^{3/2}\left(1-\frac{7}{32}%
\frac{1}{x^{3}}-\frac{1463}{6144}\frac{1}{x^{6}}-\frac{4\;95271}{3\;27680}%
\frac{1}{x^{9}}-\frac{2065\;30429}{83\;88608}\frac{1}{x^{12}}-\cdots\right).\]