Can I only submit my graduate transcript for a second-master/PhD application?
The general answer to this question is no, your undergraduate transcript is required as well.

The reason is that for master's degree programs where coursework dominates, undergraduate success is usually a good predictor of graduate success. While for PhD admissions, they don't have as much predictive value (since PhDs are about research, not classwork), it is still important to have a baseline for judgment.

In addition, the schools will want to check if you have the necessary prerequisites to undertake PhD studies. This usually requires your undergraduate transcript.