快速答案
表示打电话时，ligar 是日常通用说法；telefonar 更明确，也稍正式。
可靠的方法是先判断这个词在句子里的功能，再翻译。
每个词的作用
ligar
to call or switch on
Use ligar for making a phone call in everyday speech, as well as turning devices on.
telefonar
to telephone
Use telefonar for making a phone call, with no switch-on meaning.
如何选择
- ligar: Choose ligar if the sentence points to making a phone call in everyday speech, as well as turning devices on.
- telefonar: Choose telefonar if the sentence points to making a phone call, with no switch-on meaning.
例句
Vou ligar para minha mãe.
I am going to call my mother.
Ela telefonou para o médico.
She phoned the doctor.
常见误区
Use ligar para alguém or telefonar para alguém in standard usage. Without context, ligar may also mean turn on.
放到语境中练习
从你的真实生活中选一个句子，写两遍：一次用 ligar，一次用 telefonar。如果两个版本都可以，说明意思怎样变化。