Response

Assuming you did not obtain the working experience from your current employer, you should apply for your greencard under eb2 perm. The experience obtained from the same employer as your current one can not be used as your working experience when your current empoyer sponsors your greencard application. Given you phd background, you should insist that the company files your case under eb2 perm.

Speaking of recommendation letter, you need to obtain them from your prior employer(s) to prove that you worked for them and what your responsibilities were when you were employeed with them. Your company lawyer should have a template for the recommendation letter like this. Ask them for this.

Good luck