Phones were tapped.

这里的 tapped 不是普通的“轻拍”，而是 tap a phone 的特殊用法：

tap a phone = 窃听电话 / 监听电话

所以：

Phones were tapped.
= 电话被窃听了。
= 有人监听了电话。

句子结构

Phones = 电话
were = be 的过去式复数
tapped = tap 的过去分词
→ 一般过去时的被动语态

Phones were tapped.
= 有人窃听电话。→ 电话被窃听了。

这里没有说是谁窃听的。

再看两个例子

The police tapped his phone.
警方监听了他的电话。

His phone was tapped.
他的电话被窃听了。

所以你可以把 tap 记成两个很重要的意思：

• tap the screen = 点击屏幕
• tap a phone = 窃听电话

上下文不同，意思完全不同。