不好意思,我不懂英语,待会我叫人再打你电话.

首先,翻译不能脱离语境.
此处,楼主遇到的情况明显是他接到一外国人的电话
这种情况下,其实不能表达“不懂”英语,而是应该表达“自己的英语水平不限即懂的英语很少”所以应该如下翻译比较好：
I am sorry,my english is poor,I can not understand you very clearly,
Could you please tell me your telepone number?we'll call you back
later.
不好意思,我的英语不好,我不能很好的题解你的意思.你方便把你的电话号码留下吗?我们稍后会给你打过去(此处用"我们"其实就暗含了找一个英语不错的人打过去,不用再说ask/tell somebody to call back 了)

I am sorry , I don't understand English, can you leave your phone Number, so that I can tell somebody to call you back later.

Sorry, I'm not an English speaker,can you tell me your phone number? I'll tell someone to call you later.

楼上两个答案都不太礼貌,不符合电话用语,应该是简洁明了:
I am sorry that I don't understand English,Could you please tell me your number? I'll call back later

I am sorry that I do not understand English,Could you please tell me your telephone number? I will call back later .
希望我能帮助到你!!