1）A：你什么时候给妈妈打电话？

B：我打算吃晚饭了就给妈妈打电话。

right, but your answer could be more simple, because the question has already said what you will do.

and "我打算吃晚饭了” it means you talk on the phone while you eat, is that what you want to express? or you mean you will call your mom after dinner?

if you want to express the second meaning, you should say: 我吃完晚饭就给她打电话

2）A：你怎么到家了就睡觉？

B：我太累了。

good！

3）A：你什么时候走？

B：他来了我就走。

good！

hi! i am a native mandarin speaker！And I am finding a language partner for practicing English, if you want to practice mandarin we could help each other!

I come from Taiwan and use traditional Chinese. Here is my correction for your reference:

1）A：你什么时候给妈妈打电话？

fine, but a simple way to say is 你什么时候会打(电话)给妈妈?

B：我打算吃晚饭了就给妈妈打电话。

Do you mean after finishing your dinner or just a meal?

我打算吃完晚饭就打给妈妈 or 我打算吃完饭了就打给妈妈

2）A：你怎么到家了就睡觉？

B：我太累了。

Good.

3）A：你什么时候走？

B：他来了我就走。

Good, or 你何时要走?

Hope these suggestions are helpful for you. Good luck!

对的，但可以再简单一点

right， but it can be more simple