Can someone help me to solve this equation?

syms alpha

gamma = asin(k3 * sin(alpha)/k2);
delta_k = k1  + k2   * cos(gamma)  - k3  * cos(alpha);

phi = delta_k* l_cry;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%phase matching angle
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

eq0 =  phi==0;
Alpha = solve (eq0, alpha);
Alpha = double(Alpha);
phaseMatchingAngle =Alpha; % [rad]

I get this error:

Warning: The solutions are parameterized by the symbols: x. To include parameters and conditions in the solution, specify the 'ReturnConditions' option.

> In solve>warnIfParams (line 510)
  In solve (line 360)
  In phaseMatchingNoncollAngle_uniaxial (line 24) 
Warning: The solutions are valid under the following conditions: in(x, 'real') & (in((x + acos(100691026651348577645466123997729/101259576687255896431374526311264))/(2*pi),
'integer') & 0 <= (14308015215741192*cos(x))/3916498633832911 - 10615683778682338/3916498633832911 | in((x -
acos(100691026651348577645466123997729/101259576687255896431374526311264))/(2*pi), 'integer') & 0 <= (14308015215741192*cos(x))/3916498633832911 -
10615683778682338/3916498633832911). To include parameters and conditions in the solution, specify the 'ReturnConditions' option. 
> In solve>warnIfParams (line 517)
  In solve (line 360)
  In phaseMatchingNoncollAngle_uniaxial (line 24) 
Error using subsref