Distinction Between Meanings

Question

I'm assuming you can tell if the speaker is expressing probability through context in conversation, but if I wanted to say the below would I be correct in all context?

I'm sorry, I was probably walking when you called yesterday = Lo siento, caminaría cuando me llamaste ayer.

I'm sorry, it's possible I was walking when you called yesterday. Lo siento, es posible que estuviera caminando cuando me llamaste ayer.

I would walk when you call me on the phone = Caminaría cuando me llames por teléfono.

I think I have the tendency when speaking to use a structure more like "es posible que estuviera caminando " instead of the first. Just want to be sure both are correct and if I should start implementing the conditional simple to sound more natural. Thanks in advance!

Inma Sánchez · Accepted Answer

Hola Carter
You can use the conditional here:
Lo siento, caminaría cuando me llamaste ayer.
I'm sorry, I was probably walking when you called yesterday.
Although it would sound better if you used the conditional in the progressive form: Lo siento, estaría caminando cuando me llamaste ayer. Maybe because "caminar" conveys movement and it sounds better with the continuous form. 
Your option with es posible que... is also correct and natural and I can't see any difference in meaning with the previous one, it's simply another natural way to express the same:
Lo siento, es posible que estuviera caminando cuando me llamaste ayer.
I'm sorry, it's possible I was walking when you called yesterday. 
Other possibilities here are:
Lo siento, puede que estuviera caminando cuando me llamaste ayer.
Lo siento, quizás / tal vez estuviera caminando cuando me llamaste ayer.
Lo siento, posiblemente estuviera caminando cuando me llamaste ayer.
The difference with these last sentences and the one using the conditional is that you've got an indicator of "possibility" (puede que, posiblemente, tal vez...) on these, but with the direct use of the conditional there is no extra indicator, the use of the conditional with the main verb is what gives that nuance by itself.
Bear in mind that the conjecture needs to be about a past action, not future, so in your last sentence this wouldn't work:
Caminaría cuando me llames por teléfono. 
I would walk when you call me on the phone.
You are talking here about something that hasn't happened yet, so the use of the conditional in "caminaría cuando me llames..." doesn't work. If you want to express what "you might be doing" when they call you (later) you need to use other structures that involve the subjunctive:
Es posible que esté caminando cuando me llames por teléfono.
Posiblemente esté caminando cuando me llames por teléfono.
Puede que esté caminando cuando me llames por teléfono.
Quizás esté caminando cuando me llames por teléfono.
I'll probably be walking when you call me.
Saludos
Inma