The verbs 接 (jiē) and 接到 (jiēdào) are both used to talk about answering and receiving (e.g. with a telephone), but the way they work grammatically is different and they have different meanings.
动词"接 (jiē)"和"接到 (jiēdào)"都是用于谈论应答和接收（如电话），不过它们在语法使用上有些不同，意思也不一样。
The difference lies with 到 and the change it makes to the meaning of a verb. By comparing 接 and 接到, you'll get a gentle introduction into how 到 works and Chinese verbal complements in general.
不同之处在于和"到 (dào)"的搭配以及它改变的动词的意思。通过比较"接"和"接到"，你会稍微了解 "到"的用法以及中文动词补足语。
接 (jiē): to answer
On its own, 接 means ‘to answer' or ‘to connect'. Originally 接 does mean ‘receive', but its meaning is not as complete as ‘receive' in English. The Chinese 接 is an action verb, and only describes the attempt. We don't know from 接 alone the result of the action.
单单"接"这个字本身就是"去应答 (to answer)"或"去接触 (to connect)"的意思。"接"的最初本意是"接受"，但和英文里的"receive"又不完全对应。中文里的"接"是个行为动词，只用于描述"尝试、意图"，单单一个"接"，我们无从得知动作的结果是什么。
In the following examples, 接 is used in this way as a simple action verb:
Wǒ yào jiē gè diànhuà.
I'm going to take a phone call.
Qǐng jiē yīxià diànhuà.
Please answer the phone.
Méi rén jiē.
As you can see, whilst the action of answering or receiving a phone call is described, the result of the action isn't made totally clear.
接 can also mean ‘receive' in the sense of meeting someone, especially at a particular time and place. Have a look at some examples:
Nǐ kěyǐ lái jīchǎng jiē wǒ ma?
Can you come to the airport and meet me?
Bùyòng jiē wǒ.
There's no need to come and meet me.
Wǒ méiyǒu qù jiē tā.
I didn't go to meet him.
Notice how the action itself is described, but the actual result of the action isn't specified. The last sentence might seem like it does describe the result of 接, but look closer. It actually says that no attempt to 接 anyone was made, so there's no result.
To specify the result of what happens when you try to 接 something or someone, you need 到.
接到 (jiēdào): to receive
When you add 到 after 接, you make it clear that the action was achieved or completed. You may know that 到 means ‘arrive', and this sort of makes sense here: our action of trying to 接 "arrived" at its target destination.
Many verbs in Chinese work in this way; on their own they don't specify the result, but adding 到 (or one of a range of other result complements) makes the action complete.
Have a look at some examples with 接到:
Wǒmen hái néng jiē dào tāmen ma?
We will still be able to meet them?
Nǐ jiē dào diànhuàle ma?
Did you manage to answer the phone?
Wǒ méiyǒu jiē dào diànhuà.
I didn't manage to answer the phone.
Wǒ zài jīchǎng méiyǒu jiē dào tā.
I didn't manage to meet him at the airport.
Wǒ zài huǒchē zhàn jiē dào tāle.
I managed to meet him at the train station.
The examples have been translated into English with ‘manage to'. This is a little unwieldy, but makes the meaning of 接到 clearer.
Finally some examples directly comparing 接 with 接到:
Wǒ méiyǒu jiē dào diànhuà.
I didn't answer the phone [because I was unable to (因为我没有成功做到)].
Wǒ méiyǒu jiē diànhuà.
I didn't answer the phone [because I didn't try to (因为我没有尝试去接电话)].